In many manufacturing operations, the most efficient utilization of raw materials and equipment requires the continuous feed of a moving web of flat stock, for example, rolled paper, cardboard, floor covering and the like. To provide the web continuously, an apparatus is used to automatically splice the trailing end of an expiring roll of web material being utilized in the production process with the leading end of a fresh, replacement roll to be utilized next in the process. This is performed without interruption of the advance of the web or, for that matter, interruption of the manufacturing process itself. An implementation of a conventional apparatus of this type is taught by commonly-assigned U.S. Pat. No. 3,822,838, issued Jul. 9, 1974 and entitled "Web Handling Apparatus", the disclosure of which being incorporated herein by reference.
Basically, this conventional apparatus includes supports for a pair of web rolls, one of which is a running supply roll and one of which is a fresh roll at the ready for use next, after the running roll is depleted. The supports alternate in holding the running and ready rolls. Web is fed from the running roll, through a splicing mechanism, to an accumulator and then to a printing press or other machine which consumes the web at high speed. To assure a high quality, dependable splice, the splicing is carried out while the two webs being spliced are moving at a slow speed or are stationary. For this reason, it is commonly referred to as a "zero-speed" splice.
The web is pulled from the running supply roll by a mechanism in the web-consuming machine so that it usually moves at a constant rate whose value depends on the requirements or capabilities of the machine.
The accumulator shown in the previously-mentioned patent stores in festoon fashion an excess length of the material until such time as it is desired to make a splice. Then, during splicing, it gradually delivers the stored web to the web-consuming machine. Essentially, the accumulator is a mechanically adjustable, tortuous web path typically defined by a set of stationary rolls, each pair of which being separated along the web path by a movable roll. In other words, the web is looped between the fixed rolls and movable rolls, forming a series of bights.
The movable rolls are commonly referred to as a "dancer" and, in operation, translate in unison toward or away from the set of fixed rolls. This movement controls the amount of material in the accumulator. For example, as the dancer moves further away from the set of fixed rolls, the amount of material in the accumulator increases, and vice-versa. Typically, the dancer is biased away from the fixed rolls by a constant force, and is caused to move from a reference position by changes in tension in the web. In response to the deviation of the dancer from the reference position, the running supply roll is braked to a greater or lesser degree in a controlled fashion to return the dancer to its reference position and thus maintain the web tension within a selected range.
When it is time to initiate a splice, the splicing mechanism is actuated. In a typical instance, the ensuing splicing procedure entails several coordinated steps performed in sequence, including: stopping the rotation of the running supply roll, pressing the stationary web from that roll against the prepared leading end of the web from the fresh supply roll to make the splice, cutting the expiring web behind the splice and, finally, accelerating the fresh supply roll to bring the new web from that roll up to line speed and to replenish the accumulator. Conventionally, only after the splice is made is acceleration of the fresh roll commenced to bring the new web up to line speed.
To permit the two rolls to remain stationary during splicing without concomitantly interrupting the operation of the web-consuming apparatus, the storage capacity of the accumulator must be sufficient to meet the needs of the web-consuming apparatus during the entire splicing procedure. Of course, this means that the required accumulator storage capacity depends on the speed of travel of the web into the web-consuming apparatus. For instance, if a particular web-consuming machine has a line speed twice that of another such apparatus, twice as much web is used by the first web-consuming machine during the splicing procedure, and the accumulator of that machine must be able to store twice as much web.
By the same token, the required storage capacity of the accumulator also is dependent on the time it takes to accelerate the full roll from an angular velocity of zero to the selected running speed. It is self-evident that, until the fresh roll has reached the requisite speed, the accumulator must continue to make-up the resulting shortfall of web required by the web-consuming apparatus. The longer the acceleration takes, the larger must be the storage capacity of the accumulator. To shorten the duration of this acceleration phase of the splice sequence, some splicers incorporate a supplemental motor drive or "kicker" to overcome the inertia of the fresh roll and more quickly accelerate it to the requisite speed.
As is well known to those skilled in this art, most conventional web handling apparatus using such accumulator and roll acceleration arrangements do generally fulfill their intended purposes. However, their accumulators are large and occupy a considerable amount of floor space which is at a premium in most press rooms. Also, being composed of massive parts, they are relatively costly in their own right. Finally, because of the high inertias of their heavy moving parts, they tend to introduce tension upsets in the running web at the very high line speeds desired for present day presses, i.e., in excess of 2000 feet per minute.
As should be apparent from the foregoing discussion, the main disadvantages of prior web handling arrangements stem primarily from the length of time required to complete the entire zero-speed splice procedure including accelerating the fresh web to line speed. If normal operation at full line speed could be restored more quickly after the splice is made by, for example, finding a way to accelerate the fresh roll to line speed earlier, the accumulator size could be reduced or the line speed could be increased.